1. Field of the Invention
The present invention relates generally to an internal combustion engine and more specifically to a poppet valve control arrangement which reduces the amount of force required to open the valve, reduces the amount of abrasive wear and which induces the same to rotate during operation of the engine in a manner which prolongs the working life of the same.
2. Description of the Prior Art
Poppet valves used in internal combustion engines are usually biased to a closed position using a relatively strong spring and moved against the force of the spring by a cam, or a cam actuated rocker arm. However, with this type of arrangement a relatively large force is required to overcome the spring and lift the valve off its seat.
FIGS. 1 and 2 show two previously proposed arrangements which have attempted to reduce the amount of force which must be applied to open the valves. The arrangement shown in FIG. 1 comprises a cam shaft 1 on which a lift cam 2 and a closure cam 3 are fixedly mounted in a side by side relationship.
A rocker shaft 4 supports a lift rocker arm 5 and a closure rocker arm 6. The lift rocker arm 5 is provided with an adjust screw 7 via which the valve clearance be be adjusted.
A poppet valve 8, which can be either an inlet valve or an exhaust valve, has a stem 8a the top of which is provided with a retainer 11. The retainer 11 is formed with a radially extending flange at the bottom thereof which is arranged to be engaged by the leading or outboard end of the closure rocker arm 6. The end of the rocker arm 6 is formed with a U-shaped recess (not shown) which defines two bifurcate finger members. These fingers extend on either side of the valve stem 8a and engage the bottom of the retainer 11.
In operation, as the cam shaft 1 rotates, the lift and closure cams 2, 3 rotate to positions wherein the high and low lift portions thereof engage the lift and and closure rocker arm followers 5a, 6a. This induces the lift rocker arm 5 to rotate in a direction which brings the end of the adjust screw 7 into engagement which the top of the valve stem 8a and applies a force which tends to lift the valve head 8b off the valve seat 8c. Simultaneously, the closure rocker arm 6 is rendered rotatable in the same direction as the lift rocker arm 5, and thus relaxes the force which tends to bias the valve head 8b into engagement with the valve seat 8c.
Accordingly, the valve head 8b is lifted from its valve seat 8c and moved to an open position.
As the cam shaft 1 continues the rotate the low lift and high lift portions of the lift and closure cams 2, 3 come into contact with the followers 5a, 6a of the lift and closure rocker arms 5 & 6, respectively. This causes the closure rocker arm 6 to rotate in a direction which forces the lead end thereof against the lower face of the retainer 11 and produces a force which moves the valve 8 upwardly (as seen in the drawings) and which permits the lift rocker arm 5 to be rotated in the same direction. The valve 8 is thus moved until the valve head 8b engages the valve seat 8c and closes the valve.
In the FIG. 2 arrangement, the lift rocker arm 15 is arranged to engage a flanged retainer 21 at its leading end and to have a follower 15a formed thereon at a location distal from the axis about which it is pivotally mounted. The closure rocker arm 16 is pivotally mounted on the same rocker shaft 14 as the lift one, and provided with a clearance adjust screw 17 which is arranged to engage a portion of the lift rocker arm located proximate the shaft 14 on which the two rocker arms are pivotally mounted.
With this arrangement as the cam shaft rotates essentially the same type of push-pull type of operation which occurs in the FIG. 1 arrangement occurs and the valve is opened and closed.
For further disclosure relating to such types of arrangements, reference can be had to JU-A-61-6611, JP-A-60-32910, JP-A-60-39211 and JU-B-53-51928.
However, the above mentioned arrangements have encountered the problem that, with the passing of time, the valve heads and seats tend to undergo localized wear and/or deterioration. This as well known, leads to the loss of sealing by the valve and invites loss of efficiency and proper engine operation. They have also suffered from the drawback that both of the clearances between the lift and closure rocker arms and the portions of the valve and the retainer which they engage is difficult to set and maintain. Accordingly, these type of arrangements have tended to be noisier than the conventional spring loaded types.